The instant invention relates to seals and more particularly to a seal made from compacted wire which is particularly effective for use in high-temperature applications.
For many years, seals and gaskets containing asbestos were utilized for most high-temperature applications. However, with the discovery that asbestos has carcinogenic properties, the use of seals containing asbestos has been severely restricted, and therefore a need has developed for an effective high-temperature seal which does not contain asbestos. In this connection, although a number of materials other than asbestos have been heretofore available which can withstand prolonged exposure to high temperatures, they have generally not had sufficient resiliency and flexibility to make them effective for use in many types of gaskets. Hence, there has remained a substantial need for an effective asbestos-free gasket and/or seal construction which can be utilized in high-temperature applications and which has a certain degree of resiliency and flexibility.
Heretofore it has generally been known that seals and/or gaskets which are suitable for some applications can be made from compacted knitted-wire elements. More specifically, it has been known to form seals and/or gaskets comprising elements which are made by knitting wire to form sheets or tubular socks, rolling the sheets or socks to form rolls or rings of knitted wire and then compressing the rolls or rings to form compacted knitted-wire elements. Knitted-wire elements of this type have been utilized as the core elements for seals, wherein they are covered with fiberglass fabrics for providing reduced leakage rates. Further, it has also been known to impregnate knitted-wire elements of the above type with various types of filler materials to provide the necessary reduced leakage rates so that they can be utilized for seals and/or gaskets. However, the use of compacted knitted-wire elements for seals and/or gaskets without utilizing them in combination with filler and/or covering materials has not been feasible, since gaskets made from knitted-wire elements which have not included outer casings or filler materials have generally had excessively-high leak rates.
The instant invention relates to a seal construction comprising a compacted knitted-wire element which does not require the use of outer casings or extraneous filler materials. More specifically, the instant invention relates to an effective method of forming a compacted wire seal which is operative with reduced leak rates and to the seal itself. The method of forming a compacted wire seal in accordance with the instant invention comprises the steps of knitting an elongated wire to form a sheet of knitted wire which may be either flat or of tubular configuration and rolling the sheet to form a roll or ring of knitted wire. The method further comprises the steps of heating the roll or ring of knitted wire in an atmosphere containing oxygen to form oxides on the surfaces of the wire and to anneal the wire, and then compressing the wire in a die cavity to form a compacted wire seal. In the preferred form of the method, the wire comprises stainless-steel wire, and it is flattened before it is knitted in the knitting step. Further, in the preferred form of the method, the wire is formed into a tubular sock, and the sock is rolled on itself from both ends thereof to form two adjacent rolls. Still further, in the preferred form of the method, the heating step is carried out so that oxides are formed on the surfaces of the wire in an amount comprising at least approximately 0.025 mm.sup.3 of oxide per cm.sup.2 of wire surface; and in the compressing step the rolled wire is compressed to a density wherein it comprises at least approximately 45% by volume of wire and oxide. Still further, in the preferred form of the method, after the wire has been knitted to form a tubular sock, rolled on itself to form a knitted-wire ring, and heated to form the oxides on the wire and to anneal the wire, the ring is compressed in a die cavity to form a compacted wire-ring seal having a V-shaped cross-sectional configuration. Specifically, the seal is preferably formed so that it has a V-shaped configuration wherein the apex of the V-shape thereof is disposed on one side of the seal and the legs of the V-shape diverge from the apex to define the inner and outer extremities of the seal.
It has been found that the compacted wire seal of the instant invention which is made in accordance with the hereinabove-described method can be effectively utilized in applications wherein slow gas-leakage rates can be tolerated. In this connection, however, it has been found that because of the method by which the seal of the instant invention is made, it has substantially reduced leakage rates in comparison to gaskets made from other types of compacted knitted-wire elements. Specifically, by heating the knitted wire in an atmosphere containing oxygen after the wire has been formed into a roll or a ring, oxides are produced on the surfaces of the wire; and when the roll or ring of knitted wire is thereafter compressed, these oxides fill in some of the void areas in the compacted wire seal to reduce the leakage rates which are obtained with the seal. Further, when the knitted wire seal is formed in a V-shaped configuration, it has sufficient resiliency in the legs of the V-shape thereof to compensate for minor irregularities in the surfaces of elements with which it is positioned in engagement. In particular, when the seal is mounted so that a first element is received in engagement with the inner periphery of the seal and a second element is received in engagement with the outer periphery thereof, the V-shape of the seal and the resiliency and flexibility of the compacted wire construction thereof allow it to be maintained in sealing engagement with the first and second elements regardless of irregularities in the surface configurations thereof. In this connection, while V-shaped configurations are generally known for various types of seals, heretofore they have only been applied to positive seals having solid constructions, and they have not been applied to seals made of compacted knitted wire. Hence, the heretofore-available compacted knitted-wire seals have not been effectively able to cushion elements in the manner of the seal of the instant invention, and they have not been compressible in the manner of the seal of the instant invention.
One particular application for high-temperature seals is in catalytic converters of the type used for treating exhaust gases on automobiles, trucks, and the like. In this connection, most catalytic converters of this type comprise a ceramic monolith through which exhaust gases can pass, a platinum catalyst which is deposited on the monolith, a refractory or wire-mesh blanket which is received around the ceramic monolith, a metallic housing in which the monolith and the refractory or wire-mesh blanket are mounted, and a seal between the monolith and the housing. Further, in this connection, the housing of a catalytic converter of this type is constructed for receiving exhaust gases and for directing them so that they pass through the monolith. The refractory or wire-mesh blanket is provided for protecting and cushioning the monolith so that it does not contact the housing and fracture, and the seal of a catalytic converter of this type is provided for sealing between the monolith and the housing so that substantial quantities of exhaust gases do not bypass the monolith, although relatively low leak rates can generally be tolerated. Heretofore seals of the type comprising a compacted wire element with a fiberglass cloth sleeve thereon have been utilized for applications of this type. However, these seals have been made from elongated compacted wire elements rather than from compacted wire rings, and hence they have had seams where they have been formed into rings. These seams have been known to cause breakage in monolith elements. Further, seals of this type have not been able to effectively conform to housings in which they have been mounted, and they have also been relatively expensive.
It has been found that the seal of the instant invention can be economically made and that it is particularly effective for use in catalytic converters of the above-described type. Specifically, the seal of the instant invention, which is preferably made in a V-shaped configuration, can effectively seal between the monolith and the housing of a catalytic converter, since it can compensate for minor irregularities in the configurations of the housing and/or the monolith. Further, when the seal is constructed from stainless-steel wire, it can withstand very high temperatures which are often experienced in catalytic converters; and since the seal is formed as an endless ring without seams, it is less likely to damage a monolith element of a catalytic converter. Still further, because oxides are formed on the surfaces of the wire in the seal of the instant invention before the seal is formed into a V-shaped configuration, the seal can effectively meet the leak-rate standards for catalytic converters. Even further, since the oxides on the wire of the seal of the instant invention are actually formed on the surfaces of the wire rather than being filler materials which are added to the seal, the risk that particulate matter will escape from the seal and contaminate or clog downstream components, such as additional catalytic converter elements or monoliths, is substantially reduced.
Accordingly, it is a primary object of the instant invention to provide a method of manufacturing an effective compacted wire seal.
Another object of the instant invention is to provide an effective compacted-wire seal.
A still further object of the instant invention is to provide a method of making an effective high-temperature seal for the monolith of a catalytic converter.
An even still further object of the instant invention is to provide an effective high-temperature seal for a monolith of a catalytic converter.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.